There is a fundamental gap in understanding how cytokine milieu affects the oxidative capacity of macrophages, in general, and in neonates, in particular. Systemic and pulmonary innate immune responses are highly reliant on phagocytes and their capacity for generating reactive oxygen and nitrogen species. Reactive intermediates have a broad spectrum of activity against infectious agents, including viruses, bacteria, protozoa and fungi. Lack of production of nitric oxide and peroxynitrite by alveolar macrophages has been documented in fulminant early-onset neonatal pneumonia. The long term goal is to develop pharmacologic and immunotherapeutic strategies to specifically regulate the oxidative effector function of pulmonary macrophages. The objective of this application is to identify the cytokine profile that modulates the oxidative response of the neonatal and adult macrophage. The central hypothesis of the proposed experiments is that activated macrophages from neonates produce less peroxynitrite than those from adults. It is plausible that difference in the cytokine milieu of the macrophage plays an important role in the oxidative response of the neonatal vs. adult macrophage and that the predominant Type 2 cytokine profile of human and equine neonates plays an inhibitory role in the production of reactive intermediates. A major goal of this application is to chronicle the evolution of the cytokine milieu and oxidative capacity of pulmonary alveolar and tissue macrophages from the neonatal period through adulthood. Thus, the proposed research is relevant to that part of NIH's mission that pertains to developing fundamental knowledge that will help to prevent disease and promote the health of neonates and children. Guided by strong preliminary data, the central hypothesis will be tested by pursuing two specific aims: 1) Determine the extent to which macrophages from neonatal foals and adult horses produce reactive oxygen and nitrogen species. 2) Determine the extent to which the cytokine milieu of the macrophage affects macrophage phenotype and production of reactive oxygen and nitrogen intermediates. The proposed research is innovative because, to date, no longitudinal, in vivo, study of the acquisition of adult immunocompetency - from the neonatal period through adulthood - focusing on cytokine milieu and oxidative capacity of tissue and pulmonary alveolar macrophages has been explored. This contribution is significant because it is expected to provide the knowledge needed to (A) develop diagnostic assays that predict an individual neonate's susceptibility to pneumonia, and (B) test pharmacologic and immunotherapeutic strategies to specifically regulate the cytokine and oxidative effector function of macrophages during the neonatal period. The equine neonatal model affords study of the progressive acquisition of adult immunocompetency as pulmonary alveolar and monocyte derived macrophages may be repeatedly obtained with relative ease and in sufficient quantities for carrying out the proposed studies. In addition, the 18 month time to reproductive maturity in horses is amenable to such studies. PUBLIC HEALTH RELEVANCE: The proposed studies are of an important and under-investigated area of neonatal immunodevelopment that has the potential applicability to understanding the predilection to neonatal and childhood pneumonia as well as risk prediction for particular neonates especially susceptible. The proposed research has relevance to public health, because the fundamental mechanisms to be investigated appear to cross species lines and relate to age. Thus, the findings are expected to be applicable to the health of human neonates.